James P. Eaton MD, Presenter: Nothing to Disclose

Brian David Petersen MD, Abstract Co-Author: Nothing to Disclose

MRI is highly sensitive for the detection of marrow edema from both traumatic and non-traumatic causes. The marrow edema pattern resulting from multiple complex knee injuries has been extensively studied and reported. ACL tears often occur related to a pivot-shift mechanism that results in valgus angulation and external tibial rotation. This injury is commonly associated with a well documented “kissing contusion” pattern of edema within the anterior lateral femoral condyle and posterior lateral tibial plateau. However, the presence of marrow edema within the non-weight bearing medial femoral condyle has only seldom been reported and the mechanistic cause of the injury pattern has not been postulated.  The purpose of our study was to determine the prevalence of marrow edema within the non-weight bearing medial femoral condyle in patients with acute ACL disruption and to offer a biomechanical explanation for the finding.

A retrospective review of the MRI examinations of all patients who sustained an acute ACL tear over a 5 year period was performed to evaluate for the presence of edema within the medial femoral condyle and for evidence of injury to the medial collateral ligament.  Additional areas of marrow edema and any associated internal derangement were also recorded.  The medical record was reviewed to elucidate the mechanism of injury.

Initial data demonstrates marrow edema in the non weight-bearing portion of the medial femoral condyle in 64 of 165 (39%) acute ACL tears. Injury to the deep MCL fibers, or their attachment, was seen in 62 of 64 (97%) of patients with this MFC edema pattern. 62 of 64 (97%) of patients with MFC edema also had edema within the lateral compartment. Mechanisms of injury included pivot, twisting, valgus forces, and hyperextension.

The biomechanical properties of the deep MCL fibers predispose it to injury at a lower stess than the more superficial fibers. Bone marrow edema in the non-weight bearing medial femoral condyle may occur as a result of the traction stress on the deep MCL fibers during the pivot shift injury in 39% of acute ACL injuries.

Given the importance of recognizing marrow edema patterns in correct MRI interpretation defining this injury helps the practicing radiologist avoid misinterpretation of this injury pattern.

Eaton, J, Petersen, B, Association of Non-Weight Bearing Medial Femoral Condyle Edema with Acute ACL Tear.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12027897.html